The fact that an atom will emit a photon of radiation when one of its electrons drops to a lower energy state has enabled the laser to be employed in a number of military, industrial, and medical applications. The term “laser” is an acronym for light amplification by stimulated emission of radiation. In its simplest form, a laser consists of a rod of transparent crystal or a tube filled with gas or liquid. A reflecting mirror is placed at one end and a partially reflecting mirror at the other end. The laser is then pumped by adding energy, e.g., by shining another light source into it, by adding electrical energy, or by stimulating a chemical reaction. This process raises electrons in the laser to higher energy states.
During or subsequent to the pumping process, some of the electrons will spontaneously fall back to a lower energy state, emitting photons. The photons that travel toward the sides of the laser are quickly lost, but those traveling along the length of the rod or tube are reflected back by the mirrors. This activity generally occurs in the area commonly referred to as the laser gain region. When these photons strike other excited atoms, they stimulate those atoms to release photons of the exact same energy level (or wavelength), which travel in the same direction as the stimulating photons. The result is an intense, highly focused beam of light escaping through the half-silvered end of the laser. This light beam is generally referred to as a beam of coherent radiation, or more commonly, a laser beam.
Because the photon wavelength is determined by the characteristics of the atoms in the lasing material, laser light can be of a single wavelength. Because laser light travels in a tight beam, it can carry a great deal of energy over a great distance without significant loss. With respect to recent developments in laser technology, there has been increased interest in high-energy chemical laser systems.
Current high-energy chemical lasers can be classified as either: (1) hydrogen-halide lasers; or (2) chemical oxygen-iodine lasers (COIL). Hydrogen-halide lasers typically employ a reaction of hydrogen and/or deuterium with fluorine, chlorine, bromine or iodine in diluent gases of helium, nitrogen, or the like, to produce hydrogen and/or deuterium halide molecules in excited vibrational states from which laser energy can be extracted. Exhaust from the laser cavity of a hydrogen-halide laser is typically a mixture of gases at high temperature (up to 1000° C.) including HF (and/or DF), He, N2, and possibly small amounts of H2 (and/or D2), and other gases.
In current COIL systems, chlorine gas, with or without a diluent gas such as nitrogen or helium, reacts at low pressure with a solution of basic hydrogen peroxide (i.e., usually NaOH, KOH or other strong base mixed with hydrogen peroxide) to produce a gaseous flow of excited oxygen, also referred to as singlet delta oxygen or singlet molecular oxygen (designated as O2*, O2(1Δ), as well as by other symbols). This gaseous flow of singlet delta oxygen mixes (typically at speeds approaching or even exceeding the speed of sound) with iodine gas molecules (i.e., I2) generally mixed with a diluent gas such as nitrogen or helium, dissociating them and exciting the resulting iodine atoms (i.e., I), which lase at 1.315 μm. The major laser byproducts are various salts (e.g., NaCl or KCl), water, and heat. Exhaust from the COIL laser cavity is typically a mixture of gases at near ambient temperature, including nitrogen or helium, oxygen, and small amounts of chlorine, iodine, and water. The gas is recompressed, the small amounts of chlorine and iodine can be scrubbed from the output, and the resulting gas exhausted.
The intended operation of a conventional COIL system can be summarized as follows. The initial step is to generate the singlet delta oxygen. This is accomplished by providing a source of basic hydrogen peroxide, typically in liquid form, and a source of molecular chlorine, typically in gaseous form. These two materials are then charged or injected into a singlet delta oxygen generator through appropriate manifold/conduit assemblies, respectively. The resulting exothermic reaction between the basic hydrogen peroxide liquid and the molecular chlorine gas produces the gaseous singlet delta oxygen, as well as several by-products, such as salt and heat. The heat can be removed by appropriate devices such as a heat exchanger, and the salt can be removed by appropriate devices such as a filter, if desired.
Once the gaseous singlet delta oxygen is generated, it is then charged or injected in flow form into a mixing nozzle at the appropriate time. The mixing nozzle has a throat portion which generally divides the mixing nozzle into a subsonic zone and a supersonic zone; that is, the flow of gaseous singlet delta oxygen is subsonic in one portion of the mixing nozzle and supersonic at the other portion of the mixing nozzle. The mixing of reactants is typically done in the subsonic zone, but their mixing can be done in other zones of the gain generator.
A molecular iodine generator is in communication with the mixing nozzle by an appropriate manifold/conduit assembly. At the appropriate time, gaseous molecular iodine is then charged or injected into the mixing nozzle in such a manner so as to partially or completely mix with the singlet delta oxygen gas flowing from the singlet delta oxygen generator. The mixing permits the singlet delta oxygen to dissociate some of the molecular iodine and thereby initiate the chain reaction dissociation by the product, excited atomic iodine.
The primary reactions taking place in connection with the conventional COIL system are as follows:I2+NO2*→I2*+NO2  (1)
That is, a mole of molecular iodine reacts with several moles (denoted by the symbol “N”) of singlet delta oxygen to produce a mole of excited molecular iodine and several moles of molecular oxygen.I2*+O2*→2I+O2  (2)
That is, a mole of excited molecular iodine reacts with a mole of singlet delta oxygen to produce two moles of atomic iodine and a mole of molecular oxygen.I+O2*→I*+O2  (3)
That is, a mole of atomic iodine reacts with a mole of singlet delta oxygen to produce a mole of excited atomic iodine and a mole of molecular oxygen.I*+hv→I+2hv.  (4)
That is, a molecule of excited atomic iodine interacts with a photon and releases a second photon (hv), thus producing a molecule of atomic iodine.
The singlet delta oxygen gas flow initially contacts the gaseous molecular iodine gas at subsonic speed; however, the singlet delta oxygen gas flow is quickly brought up to near supersonic or even supersonic speed (via appropriate devices such as a venturi) and is expelled out through the mixing nozzle into the area known as the laser cavity or laser gain region. It is in this area where the excited atomic iodine releases its photon. The released photons are then reflected between a set of mirrors, the first mirror being fully reflective, the second mirror being partially reflective. The reflected photons eventually form a laser beam, which is transmitted through the partially reflective mirror at a wavelength of 1.315 μm. Any remaining chemical species are removed from the laser gain region by a combination of exhaust assemblies and scrubber assemblies in order to avoid contamination of the laser's mirrors and to allow continuing flow of the laser chemicals so as to sustain the lasing process.
One particular application of chemical laser systems that is of significant interest is in space-based lasers (SBL's). As part of a ballistic missile defense system, SBL's have the potential of intercepting and destroying enemy missiles prior to them reaching their intended targets. An SBL system would achieve missile interception by focusing and maintaining a high powered laser on a target until it achieves catastrophic destruction. Because the SBL system typically requires very large amounts of laser power to achieve it's operational objectives, it is unlikely that an electrically driven laser system would be a practical source of power, at least for the foreseeable future. However, it is generally believed that the amount of energy needed for the sustained laser burst can be produced by currently available COIL systems.
Unfortunately, an SBL system employing a COIL system necessarily means that the COIL system would have to rely on the limited amount of chemical supplies on board the vehicle at the time of launch. However, the COIL system would require resupply of those particular chemicals, especially basic hydrogen peroxide, chlorine, iodine, and nitrogen, after the SBL has conducted it's missile destruction mission. As the SBL systems are to be deployed in orbit above the Earth, rapid and frequent resupply of these chemicals would be highly problematic even under ideal conditions, and would be especially difficult during and immediately after any type of prolonged ballistic missile exchange. Accordingly, current SBL system designs which employ COIL systems have no means of resupplying the chemicals required for COIL system operation. Thus, the resupply problem has been identified as a significant impediment to future development and deployment of the SBL system.
While the difficulty of resupply may not be as extreme as for an SBL system, there are numerous other applications for COIL lasers for which fuel resupply is complex, costly, and difficult. For examples, COIL lasers may be used in ground and airborne applications, where fuel resupply may be hindered by location and weight restrictions.
Therefore, there exists a need for a system for collecting, reprocessing and recycling the spent chemical species required by a COIL system, especially one that is used in conjunction with either a ground-, airborne-, or space-based laser weapon system, irrespective of the source of the spent chemical species.
U.S. Pat. No. 3,992,685 discloses a chemical laser including a laser pump which is relatively lightweight with no moving parts. This produces a low pressure, regenerable, closed system for treating laser cavity exhaust gases to remove (i.e., pump) them from the system. The exhaust gases which emerge from the laser cavity of the chemical laser are pumped by reacting them preferably with titanium, titanium-zirconium alloys, zirconium, tantalum, etc. These gases include hydrogen, deuterium and their halides, the halogens, oxygen, CO2, nitrogen and H2O.
U.S. Pat. No. 4,028,069 discloses that contaminants, such as water and hydrogen sulfide, are removed from hydrocarbon streams by the use of beds of solid adsorbents including molecular sieves. The adsorbents are regenerated by heating, with the heating being performed in a closed-loop operation wherein a small quantity of the hydrocarbon being treated is recycled in a closed-loop recirculation system comprising the adsorbent and a heater until the adsorbent reaches an effective regeneration temperature.
U.S. Pat. No. 4,188,592 discloses a closed cycle chemical laser adapted for continuous wave operation. A first gas such as sulphur hexafluoride is decomposed by an electrical discharge means to provide at least some fluorine atoms which when combined with molecular hydrogen in a mixing chamber located upstream of and proximate to an optical power extraction chamber forms an excited laser species capable of stimulated emission to produce a continuous wave output beam. After passing through the optical cavity the effluent is purified by selective absorption and adsorption processes to eliminate the laser species from the effluent and to separate the hydrogen for recirculation back to the mixing chamber. The remaining effluent has its pressure increased, is supplemented with makeup feed gases and is recycled.
U.S. Pat. No. 4,357,309 discloses an apparatus and method for generating on demand a gaseous product from a liquid phase reaction of one reactant in the solid phase at ambient room conditions and another reactant in the liquid phase at ambient room conditions. The reactants preferably are iodine crystals, and liquid tetrahydronaphthalene (THN), with the gaseous product being hydrogen iodide. The liquid phase reaction, in the preferred embodiment, is 2I2+C10H12ζ4HI+C10H8, known per se. Preferably, THN is pumped from a reservoir to be sprinkled over the iodine crystals in another reservoir. Some iodine dissolves into the liquid THN, with the resulting solution then percolating through a reaction zone containing a heated, porous packing material. Heat is transferred to the solution, thereby promoting, i.e., driving the above reaction. The gaseous hydrogen iodide is then removed from the reaction zone; typically for direct use, for example, in a chemical laser.
U.S. Pat. No. 5,974,027 discloses a high energy chemical laser capable of being operated in an aircraft to interdict and destroy theater ballistic missiles. A key to the chemical laser of the invention is the use of individual chemical lasers whose individual photon energy outputs can be combined into a single high-energy laser beam.